The Constitution states that the national symbols of Ukraine
shall be the National Flag, the National Emblem and the National
Anthem.
The Ukrainian flag consists of two horizontal stripes of equal
width. The top is blue, the bottom - yellow. Blue and yellow, the
colors of the sky, mountains, streams, and golden fields have
symbolized Kyivan Rus' long before the introduction of
Christianity. With the acceptance of Christianity, blue and gold
were incorporated into church symbolism. After the Mongol-Tatar
invasion in the 1200's the use of blue/gold was interrupted, to
be revived again in church ornaments and city crests some time
later. The emblem of the city of Myrhorod, for example, was a
gold trident over a blue background. Another city, Pryluky, used
the head of an ox in gold over a blue background as its insignia.
And in Lubny, the city emblem pictured a hand holding a golden
mace over a blue background. The banners of the Cossacks (17th
Century) were blue with gold stars, a gold cross, or with
pictures of saints rendered in gold.
The blue and yellow flag as the national flag of Ukraine by the
Supreme Rada in 1992.Dov Gutterman, 10 July 2000

The blue-yellow flag was firstly displayed in Lviv (Lvov,
Lemberg) in 1848. Orenburg, for example, have blue-yellow CoA
too, But it is not in Ukraine. Banners of Cossacks were
different: blue, red, dark-red, green and other.Victor Lomantsov, 10 July 2000

In Sweden there is a story going around, stating that the blue
and yellow of Ukraine come from the blue and yellow of Sweden.
When King Carl XII of Sweden (he was king 1697-1718) went to war
against Peter the Great of Russia, he made allies with the
Ukranians, who wanted sovereignity from Russia. The Ukrainians
should therefore have taken up the colours of Sweden as their
colours. However, I don't know if there is any truth in this
story.Elias Granqvist, 10 July 2000

The Open Media Research Institute reported that on 3 September
1996 the Ukrainian Parliament (Verkhovna Rada) had approved the
country's national symbols as specified by the constitution
[OMRI, #171, 1996]. Parliament also decided to organise a
competition on the design of the state arms and the words of the
national anthem. The 'tryzub' (trident) is the state arms, and
the competition will decide the details of the design. The new
constitution was adopted by Parliament 28 June 1996 (the date was
declared a national holiday) and only confirmed the national
symbols that were already in use [OMRI, #204, 1996]. OMRI offered
no details on the action of the parliament, nor did they give any
descriptions of the symbols. Article 20 of the constitution
states that the 'The description of the state symbols of Ukraine
and the order of their use is determined by law' [IFES]:

"ARTICLE 20.
The state symbols of Ukraine are the State Flag of Ukraine, the
State Emblem of Ukraine and the State Anthem of Ukraine. The
State Flag of Ukraine is a banner made from two equal horizontal
blue and yellow fields. The Great State Emblem of Ukraine shall
be determined in accordance with the Small State Emblem of
Ukraine and the Emblem of the Zaporiz'ke Viys'ko (Zaporizhzhya
Cossacks Army) by law, which shall be adopted by no less than
two-thirds of the Constitutional membership of the Verkhovna Rada
of Ukraine. The main element of the Great Emblem of Ukraine is
the Sign of the State of Prince Volodymyr the Great (the Small
State Emblem of Ukraine). The State Anthem of Ukraine is the
national anthem with the music of M.Verbytskiy and words,
confirmed by law, which shall be adopted by no less than
two-thirds of the constitutional membership of the Verkhovna Rada
of Ukraine. The description of the state symbols of Ukraine and
the order of their use is determined by law, adopted by no less
than two-thirds of the constitutional membership of the Verkhovna
Rada of Ukraine. The capital of Ukraine is City of Kyiv."

Ukraine declared independence from the USSR on 24 August 1991.
MPs celebrated the event by carrying a huge light blue and yellow
flag through the assembly hall of the Parliament [Ukrainian
Weekly, 1996]. Ukrainians approved the independence proclamation
in a referendum held 1 December 1991. Provisional legislation [W.
Smith, 1992] concerning the flag was adopted on 4 September 1991,
with opposition from the Communists. This legislation therefore
also made the Soviet era flag official, and the two flags were
hoisted side by side (even on the same flag pole). The light blue
over yellow flag was in proportions 1:2. The situation was
changed 21 January 1992, when the light blue and yellow flag
became the only flag of Ukraine. The proportions of the flag were
then set to 2:3. The trident arms were adopted on 19 February
1992 [W. Smith, 1992].